Universal Serial Bus (USB) protocol is typically used for data communication between two devices via a USB cable that includes VBUS, D+ and D− pins. VBUS is a power pin and D+/D− pins are used for data communication. However, these pins also enable a connected device to be charged or powered up. In a normal charging operation, the connected device acquires the charge from an adaptive charger via the VBUS pin. However, prior to power negotiations, the connected device needs to detect the absence or presence of a charger attached to the connected device. The standardized charging protocol ensures proper power navigation from the charger to the connected device. But an excessive disturbance in the ground plane of the charger can interfere with the detection of the connect/disconnect status of the charger by the connected device.
The native charger for a device often has a special signature on the data pins to let the connected device know it is safe to charge with more current. This signature may come in the form of a specific voltage placed on D+, or D−, or both. Therefore, a ground shift that interferes with an accurate measurement of voltage at these pins may prevent fast charging.